A parallel-flow heat exchanger is widely used in, for example, vehicle air conditioners or outdoor units of air conditioners for buildings. The parallel-flow heat exchanger has a configuration in which a plurality of flat tubes are arranged between a plurality of header pipes such that a plurality of refrigerant passages in the flat tubes communicate with insides of the header pipes, and fins such as corrugated fins are disposed between the flat tubes.
FIG. 9 shows one example of a conventional side-flow type parallel-flow heat exchanger. In FIG. 9, the upper side of the plane of the figure is the upper side of the heat exchanger, and the lower side of the plane of the figure is the lower side of the heat exchanger. In a heat exchanger 1, two perpendicular header pipes 2 and 3 are arranged parallel to each other at an interval in the horizontal direction. Between the header pipes 2 and 3, a plurality of horizontal flat tubes 4 are arranged at a predetermined pitch in the perpendicular direction. Each of the flat tubes 4 is an elongated metal member formed by extrusion and has inside thereof refrigerant passages 5 for a refrigerant to flow therethrough. The flat tubes 4 are arranged with the extrusion direction thereof, which is also the longitudinal direction thereof, set to be horizontal, and thus a direction in which a refrigerant flows through the refrigerant passages 5 is also horizontal. A plurality of refrigerant passages 5 of the same sectional shape and area are arranged in the depth direction in FIG. 9, so that a perpendicular section of each of the flat tubes 4 has a harmonica-like shape. Each of the refrigerant passages 5 communicates with insides of the header pipes 2 and 3. Corrugated fins 6 are disposed between adjacent ones of the flat tubes 4.
The header pipes 2 and 3, the flat tubes 4, and the corrugated fins 6 are all made of a metal having high thermal conductivity, such as aluminum. The flat tubes 4 are fixed to the header pipes 2 and 3 by brazing or by welding, and the corrugated fins 6 are fixed to the flat tubes 4 also by brazing or by welding.
In the heat exchanger 1, refrigerant gates 7 and 8 are provided only on the header pipe 3 side. Inside the header pipe 3, two partition plates 9a and 9c are provided at an interval in the vertical direction. Inside the header pipe 2, a partition plate 9b is provided at a height intermediate between heights at which the partition plates 9a and 9c are provided, respectively.
When the heat exchanger 1 is used as an evaporator, a refrigerant flows in through the lower refrigerant gate 7 as shown by a solid line arrow in FIG. 9. The refrigerant that has entered through the refrigerant gate 7 is blocked by the partition plate 9a to be directed to the header pipe 2 via some of the flat tubes 4. This flow of the refrigerant is indicated by a left-pointing block arrow. The refrigerant that has entered the header pipe 2 is blocked by the partition plate 9b to be directed to the header pipe 3 via different ones of the flat tubes 4. This flow of the refrigerant is indicated by a right-pointing block arrow. The refrigerant that has entered the header pipe 3 is blocked by the partition plate 9c to be directed to the header pipe 2 again via still different ones of the flat tubes 4. This flow of the refrigerant is indicated by another left-pointing block arrow. The refrigerant that has entered the header pipe 2 turns around to be directed to the header pipe 3 again via still different ones of the flat tubes 4. This flow of the refrigerant is indicated by another right-pointing block arrow. The refrigerant that has entered the header pipe 3 flows out through the refrigerant gate 8. In this manner, the refrigerant flows from bottom to top forming a zigzag passage. The herein described case of using three partition plates is merely an example. The number of partition plates used and a resulting number of times the flow of a refrigerant turns around can set arbitrarily as required.
When the heat exchanger 1 is used as a condenser, the flow direction of a refrigerant is reversed. That is, a refrigerant enters the header pipe 3 through the refrigerant gate 8 as shown by a dotted line arrow in FIG. 9 and then is blocked by the partition plate 9c to be directed to the header pipe 2 via some of the flat tubes 4. In the header pipe 2, the refrigerant is blocked by the partition plate 9b to be directed to the header pipe 3 via different ones of the flat tubes 4. In the header pipe 3, the refrigerant is blocked by the partition plate 9a to be directed to the header pipe 2 again via still different ones of the flat tubes 4. In the header pipe 2, the refrigerant turns around to be directed to the header pipe 3 again via still different ones of the flat tubes 4. Then, the refrigerant flows out through the refrigerant gate 7 as indicated by another dotted line arrow. In this manner, the refrigerant flows from top to bottom forming a zigzag passage.
When a heat exchanger is used as an evaporator, moisture in the atmosphere condenses on the cooled surface of the heat exchanger, and thus condensate water is formed. With a parallel-flow heat exchanger, if condensate water stays on the surfaces of flat tubes or of corrugated fins, a sectional area of an air flow passage is reduced due to the water, resulting in degraded heat exchange performance.
Condensate water turns into frost on the surface of the heat exchanger if the temperature is low. This process may even proceed from frost to ice. In this specification, the term “condensate water” is intended to encompass so-called defrost water, namely, water resulting from melting of such frost or ice.
Accumulation of condensate water is problematic particularly in a side-flow type parallel-flow heat exchanger. Patent Document 1 proposes a measure to promote drainage from a side-flow type parallel-flow heat exchanger.
In the heat exchanger disclosed in Patent Document 1, drainage guides are disposed in contact with corrugated fins on a side of the heat exchanger where condensate water gathers. The drainage guides are linear members and disposed to be tilted with respect to flat tubes. At least one of both ends of each of the drainage guides is led to a lower-end side or a side-end side of the heat exchanger.